1. Field of the Invention
This invention relates to electrical receptacle and more particularly, to an electrical receptacle which contains a shutter behind the receptacle slots, which must be oriented to an open position to allow full insertion of an electrical plug. This receptacle is of a design childproof in nature.
2. Description of Prior Art
Electricity, as a source of power, has been present in American households for over a century. Electrical appliances utilize this power to perform specific functions ranging from illumination, entertainment, information handling, and/or a wide variety of work tasks. The most common means to connect the electrical device to the source of power; apart from hard wiring the device directly into the electrical circuit, is to use what has become known as electrical receptacles. These electrical receptacles consist of electrically energized female contacts into which pronged plug members of the electrical device must be inserted.
Receptacles of this nature have long been recognized as a potential source of shock hazards to children who intentionally, out of curiosity, insert metallic objects into the receptacle slots. As a result, a very large number of safety receptacles have been invented to reduce this danger. One safety receptacle version which has been invented contains a shutter behind the receptacle slots which allow entry of the pronged electrical plug only if all plug prongs are inserted simultaneously. This eliminates the possibility of a child intentionally probing the electrical contacts with a singular object. Such a receptacle shutter mechanism may be found in U.S. Pat. No. 4,379,607, Wade R. Bowden. The shutter mechanism utilized in this safety receptacle version consists of two interdependent, cam integrated, plug prong actuated members which open during insertion of the plug. These receptacles serve the purpose described, but are limited in marketing aspects due to high manufacturing expenses and poor durability.
Other childproof receptacles proposed contain a sliding or rotating flat member which moves in a plane parallel with the face plate of the receptacle. Such a member has slots incorporated within it which must be aligned with the slots of the electrical contacts. This category is fairly large with distinctions between manually movable members such as U.S. Pat. No. 4,206,957, Melvin S. Ludwig; or U.S. Pat. No. 4,768,965, Yen C. Chang, or automatic barriers which move as a result of contact between an angled cam surface, and the ends of the entering plug prong or prongs. An example of such a design may be illustrated by U.S. Pat. No. 2,545,536, Charles T. Von Holtz. Note that with these designs, a singular metallic object may be inserted into any one of the electrical receptacle contacts, although the procedure to do so may be beyond the normal capability of a child.
Additionally, there are further distinctions among cam style versions as pertaining to the ability of the receptacle to allow, or disallow entry of the plug based upon whether a third ground prong may or may not be present. An example of such a design utilizing a pivoting cam surface to do so may be found with U.S. Pat. No. 3,363,215, Clarence M. Smith.
Furthermore, completely different approaches may be discovered when searching for safety receptacles. Some of these products are essentially standard receptacles housed within some type of enclosure or box like structure which reduces the likelihood of children gaining access to the live contacts. An example of such a design is illustrated by U.S. Pat. No. 4,586,765, Thomas E. Ban. Another product, which is perhaps the most widely used method to reduce shock hazards from electrical receptacles to children, would involve the insertion of a plastic, nonconducting dummy plug into the receptacle slots. This blocks entry of an object into the receptacle slots in an economical, although cumbersome manner.
Finally, inconsequential to this invention, one other device used to prevent possible fatal electrical shocks is to wire the circuit to a device known as a ground fault circuit interrupter. This is a very useful device, but suffers a serious drawback because although it will protect against line to ground faults, it will not protect against line to line hazards. Such line to line shocks may occur when a finger (or fingers) of an ungrounded person is simultaneously in contact with both the neutral, and positive plug prongs. The current in both lines while the shock under this scenario is being experienced is equal, as when any electrical load is present; and in order to trip the device off, a line to line imbalance of approximately five milliamperes must be present. Threshold settings below this value are likely to cause occasional nuisance tripping of the device due to cumulative tool/appliance leakage or leakages from extremely long circuits. Typical response time of ground fault circuit interrupters is one fortieth of a second.
Two other drawbacks of ground fault circuit interrupters are that a power plug insertion technique is not required, and that these devices can be relatively expensive for the consumer.